Over the last few decades the utilization of abrasive jetting to create perforations in a subterranean wellbore has increased significantly. More recently the introduction of coiled tubing as a conduit means of the abrasive slurry (as opposed to jointed pipes) has allowed for faster interventions. In order to improve the efficiency on these jobs the requirements have changed and allowed for fracturing a formation with the coiled tubing remaining in the hole while the slurry is pumped to the formation through the annulus between the coiled tubing or jointed pipe and the tubing or casing.
This process was further improved by separating the fracturing stages of a formation with a plurality of pay zones with the placement of a sand plug at the end of the previous fracturing stage, which was never a precise science and could often result in a sand plug being higher or lower than the intended final plug height. This high plug prevents the next stage from being jetted and pumped without performing a remedial operation to adjust the sand plug height. The ability to circulate this sand plug (or the excess of it) with coiled tubing was further enhanced by the use of a reverse circulation valve as part of the coiled tubing bottom hole assembly (BHA), which allows for reverse circulation of the excess sand, or the placement of a new extra sand plug. In some cases, this procedure disadvantageously requires tripping the coiled tubing out of the hole for replacing the BHA with one that allowed that kind of circulation.
At the same time, there were some challenges in regards to depth correlation with coiled tubing and the abrasive jetting nozzle depth, due to stretching and shrinking of the coiled tubing due to several downhole parameters such as temperature, pressure, deviation, and friction, among others, that made the depth control of the nozzle depth very imprecise, which could possibly yield to jetting at the wrong depths. This depth correlation issue has been addressed differently by the industry, initially with correlation runs (running the coiled tubing in hole and pulling out of hole to verify depth) using some sort of correlation device (such as electronic memory casing collar locators, nipple locators or tubing end locators, real-time depth correlation devices based on pumping pressures being choked at the presence of each collar), or in some instances a mechanical device for casing collar location was used during the treatment that would require such item to be placed below the perforations as its external diameter would be very close to the tubing or casing inner diameter and would not allow for fracturing fluid around and/or past it, posing a threat to having the coiled tubing BHA stuck in the hole with proppant packed around the locating device. In general the industry does not have a solution for the depth control and for the wellbore circulation problem in a single trip in the hole.
It is desirable to provide an improved process for depth correlation and wellbore circulation during abrasive jetting and fracturing operations.